This invention relates in general to apparatus for retaining a die set in a press and in particular to a system for changing die sets in a press.
Punch presses in most metal manufacturing plants utilize a die set which comprises a metal, lower die plate mounted to a bottom plate or bed of a punch press and a similar, upper die plate mounted in vertical alignment with the lower die plate to the upper plate of the punch press. The bottom plate or bed of the press is commonly called a bolster and the upper plate of the press is also known as a ram or master plate. The ram generally lowers repeatedly upon the bolster plate, compressing a work piece between the die halves. The upper die plate of the die set and lower die plate of the die set have fixed thereon, respectively, a male punch and a female die bottom for receiving the punch. Also, the upper and lower die plates are kept in vertical alignment by die rods, also called guide posts, fixed intermediate the plates and along which the upper die plate can travel to compress a work piece placed between the punch and the die. Proper alignment of the die set with respect to the bolster and ram is crucial to efficient and safe operation of the punch press. Proper alignment of the die set on the press orients the working area of the die set with respect to the feeder assembly so that the stock is accurately fed into the press. Further, if the die set is not properly aligned over the vertical and horizontal axis of the press, an unequal burden will be placed on the press and the load will not be evenly distributed across the ram. Proper alignment of the die set in the punch press allows for the necessary slug or scrap clearances after the die has operated on the work piece.
Die sets mounted in a power press are usually changed everytime a different type of press work is desired. Generally, changing a die set on a punch press requires a skilled technician and may take over an hour in time. Once the die set has been changed, a sample run of the press is conducted to make sure the die set is properly aligned.
Conventional methods and apparatus for aligning die sets in a punch press involve the use of bolts and shims to secure the dies to the bolster plate and ram. The alignment procedure involves placing the lower die plate on the bolster and selecting the correct amount of shims for the die depth. Bolts are used to secure the die to the bolster plate by mating the bolts with threaded openings provided in the bolster plate. Until the die set is bolted to the bolster plate, it is able to be moved with respect to it. The upper die plate of the die set is secured to the ram in a similar manner. Since the die set is moveable with respect to the bolster and the ram prior to bolting, proper alignment of the die set is difficult to achieve and is time consuming. Such alignment often requires a skilled technician to set up the press when a die change is necessary. Often, slight misalignment of the dies occurs resulting in the mismanufacture of parts. Thus, not only is a large degree of time required to set up the die sets, but sample runs of parts must be made to insure that there are no misalignments. If the die sets are not properly aligned, the punch press must again be shut down for additional alignment. In a factory that runs a number of punch presses, changing over the die sets on each press can involve a considerable amount of down time to the plant as a whole, especially where each press has a limited run of differing items.
The patent to Nakamura, U.S. Pat. No. 4,397,094, illustrates one method and apparatus for locating a die set in a press, however, it requires the proper alignment of four locating pins in openings on the plates and their assembly with a jig. This involves a substantial amount of effort and time even though it appears to be an improvement over the conventional method.
Thus, there is a need in the field for an apparatus and system for quickly and efficiently changing die sets in a punch press. Further, there is a need in the field for a system that will allow a positive alignment of a die set without the need of a skilled technician and without the need for a sample run to check alignment.